1. Field of the Invention
The present invention relates to a method of manufacturing a printed wiring board which is splittable across a slit and a plurality of perforations.
2. Description of the Prior Art
There is presently such a conventional printed wiring board which is provided with a slit and a plurality of perforations in the course of the manufacturing process in order that main regions of the substrate can be separated from each other.
FIG. 3 illustrates a conventional printed wiring board 1 typical of the printed wiring board having the structure cited above. This conventional printed wiring board 1 consists of a main substrate 3 mounting a printed wiring circuit 2 which contains the predetermined pattern, and a split-table substrate 4 which is to be split from the main substrate 3. This conventional printed wiring board 1 is provided with a slit 5 and a plurality of perforations 6 between the main substrate 3 and the splittable substrate 4.
While forming the slit 5 and perforations 6 in the course of manufacturing a conventional printed wiring board as described above, cracks are easily generated between the perforations 6 or between the slit 5 and the perforations 6, thus causing the main substrate, 3 to be separated from the splittable substrate 4. Typically, the slit 5 and the perforations 6 are furnished to the printed wiring board 1 by means of a pressing and punching operation. However, as shown in FIG. 4 , when sandwiching the printed wiring board 1 between the top and bottom molds 7 and 8, a substantial difference in thickness results between superficial areas 3a, 3b, 4a, and 4b, and those superficial areas 7a and 8a of the main and splittable substrates 3 and 4 in contact with the top and bottom molds 7 and 8.
The above difference is caused by (1) the presence or absence of the printed wiring circuit 2 on those regional surfaces 3a, 3b, 4a, and 4b of the main substrate 3 and the splittable substrate 4, and (2) the difference in thickness between those superficial regions 3a, 3b, 4a, and 4b of the main and splittable substrates 3 and 4 in contact with the top and bottom molds 7 and 8 due to the presence or absence of the undercoated or overcoated insulative film or shielding film.